The present invention relates to a device for measuring the parameters of fluids treated during medical procedures. More specifically, the invention relates to a system for air detection as well as pressure monitoring in the arterial and venous blood treated in an extracorporeal cycle during dialysis treatment. In addition, measurement of the blood volume and blood temperature are also carried out by the invention.
German Patent No. 38 27 553 C1 describes a device for measuring the change in the intravascular blood volume during blood filtration in a blood purification device. At least one ultrasonic sensor is provided in the extracorporeal blood cycle, and is connected to an analyzer unit. At the start of filtration, a first ultrasonic signal is recorded and the change in ultrasonic signals is determined during filtration. The change in hematocrit is determined from the change in ultrasonic signals, permitting a determination of the change in intravascular blood volume. The measurement is based on the relationship between the velocity of sound in the blood and the protein content in the blood.
German Patent No. 44 19 593 A1 describes a device for noninvasive measurement of the pressure of a medium. This device is constituted of a pressure measurement chamber through which blood, for example, is passed. The pressure measurement chamber has a passage which is sealed by a membrane. Beneath the membrane is a rubber ring against which a pressure sensor is pressed, so that both positive and negative pressures can be measured.
European Patent No. 0 392 897 A2 describes a glass fiber sensor with which pressure, temperature and flow rate can be measured. The glass fiber is terminated at one end with reflective and temperature-dependent materials. The quantity of light reflected in the fiber is proportional to the pressure against the terminated element.
European Patent No. 0 130 441 B1 describes a pressure measurement device, where contact between a pressure chamber and a pressure sensor is ensured by suction applied to the pressure chamber against the pressure sensor. The pressure sensor thus can measure the pressure changes in the pressure chamber.
During a dialysis treatment, it is necessary to measure all the above-mentioned parameters. Conventionally, several of these measurement devices must thus be provided, requiring specialized connections between the measuring machines and the extra corporeal blood cycle. This results in a considerable expense to obtain the measurements.
The present invention is directed to a sensor device capable of measuring all the parameters necessary for monitoring treatment of medical fluids using a single, common measurement head, that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Other advantages of the invention will be realized and obtained by the apparatus and method particularly pointed out in the written description and claims hereof, as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described, the invention is a device for measuring selected parameters of medical fluids that includes a measurement chamber through which the fluid flows, sealed on at least one side by a flexible membrane, a measurement plate having a peripheral seal on an outer edge, in contact with the flexible membrane, at least one sensor for measuring the selected parameters of the medical fluid disposed on the measurement plate, and a continuous inlet formed in the measurement plate leading to the flexible membrane, so that a vacuum can be established between the measurement plate and the flexible membrane.
According to the present invention, the device includes a measurement chamber through which passes the fluid on which the measurement is to be performed. The measurement chamber is sealed with a flexible membrane on one wall, and a measurement plate which has a peripheral seal on its outer edge is in contact with the flexible membrane. At least one sensor for measuring a parameter of the medical fluid is mounted on the measurement plate. The measurement plate has a continuous inlet leading to the flexible membrane, through which a partial vacuum can be established between the measurement plate and the flexible membrane.
Several sensors can be mounted on the measurement plate, and since the flexible membrane can be brought in close contact with the measurement plate, the medical fluids are separated from the sensors on the measurement plate only by the flexible membrane. Because of the peripheral seal disposed on the measurement plate, the flexible membrane can be brought in close contact with the underside of the measurement plate by applying a vacuum, so that very close contact can be established between the sensors and the specimen of medical fluid in the measurement chamber. The contact surface of at least one sensor is preferably flush with the underside of the measurement plate, so that it is possible to establish direct measurement contact between the respective sensor and the flexible membrane.
Because of advances in miniaturization and integration technology of sensors, it is possible to arrange multiple sensors on an area a few square centimeters in size. Each respective sensor is preferably mounted in a recess in the measurement plate, with the measurement surface of the sensor being in flush contact with the underside of the measurement plate. The sensors are preferably securely glued to the measurement plate.
In particular, a pressure sensor and a temperature sensor may be used in the invention. Pressure sensors have become available formed on individual semiconductor chips due to advances in integration of Microsystems, so that the chips carrying the sensor are only a few square millimeters in size. Because the sensor surface can be brought in direct contact with the membrane, it is possible to measure both positive and negative pressures. As a result, the thermal energy balance and the venous pressure in a dialysis machine can be measured with the pressure sensor and the temperature sensor according to the invention.
According to another embodiment of the present invention, another measurement plate with a peripheral seal on its edge is provided, and is kept at a selected distance from and substantially parallel to the first measurement plate by means of spacers. The measurement chamber is then inserted between the two measurement plates. One side of the measurement chamber is formed by a second flexible membrane forming a seal with the additional measurement plate. Each measurement plate has a continuous inlet leading to the respective flexible membrane, so that a vacuum can be created between each of the measurement plates and the flexible membranes.
Because of the use of parallel measurement plates, an ultrasonic propagation time measurement can be performed, with an ultrasonic sensor being mounted on one of the measurement plates for this purpose. An ultrasonic pulse is emitted by the ultrasonic sensor, is reflected by the opposite plate, and then is received back by the ultrasonic sensor. The spacers guarantee that there is no change in the distance between the two measurement plates, so that very accurate ultrasonic propagation time measurements can be performed.
The parallel measurement plates can also be used to perform transit measurements on the specimen. To do so, at least one transmitting element is mounted on one measurement plate, and at least one receiver element paired with the transmitting element is mounted on the other measurement plate. The transmitting element may include, for example, an ultrasonic transmitter, a light source, or other transmission device. The receiver element can include a corresponding ultrasonic receiver, a light receiver, or other receiving device mounted on the opposite plate.
According to one exemplary embodiment, the ultrasonic measurement method can be carried out using opposite ultrasonic sensors to determine the relative blood volume of the fluid in the measurement chamber. The device according to the present invention also makes it possible to avoid the use of an expensive measurement chamber, such as one made of glass, that is used in conventional devices to ensure a constant distance between ultrasonic elements. Instead, a constant distance between the measurement plates is ensured by spacers.
In addition, with the present invention it is also possible to detect air bubbles in the fluid specimen being measured, using opposing ultrasonic sensors.
An optical detector formed of a light source and a light receiver may also be used, for example in the automatic detection of the presence of blood, or for detection of air bubbles.
In one preferred embodiment, the seal of the measurement plate is made of a rubber ring which is inserted into a groove in the measurement plate and projects slightly above the edge of the measurement plate. As soon as a vacuum is established between the membrane and the measurement plate, the membrane is pressed tightly against the underside of the measurement plate by the ambient air pressure, and the seal guarantees that no additional air can flow into the area between the measurement plate and the flexible membrane.
The flexible membrane can be made, for example, of a thin plastic film, while the measurement chamber may be made of a plastic chamber with rigid walls. It is especially advantageous if the flexible membrane and the measurement chamber are integrated into a disposable plastic part. Centering holes may be provided in the disposable part so that the spacers engage in them and thus reliably and securely position the disposable part with respect to the measurement plates.
The respective measurement plates are preferably made of a metal disk into which the respective sensors are inserted. In a preferred embodiment, the metal disk is kept at a constant temperature by, for example, Peltier elements. This design permits a more accurate temperature measurement of the respective specimen.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.